1. Field of the Invention
The present invention relates to a zoom lens assembly capable of effecting both macro (close-up) photography and normal photography, and particularly relates to such a zoom lens assembly of a simple structure.
2. Description of Prior Art
It is well known that, due to the limited space, photographing lenses used in camera phones have dimensions much smaller than those in photographic cameras, video cameras and digital cameras. To obtain the best image quality, camera phones generally employ fixed focal length lenses. However, since the focal length is fixed rather than adjustable, the focus range for such fixed focal length lenses is limited, and thus it would be unavailable to take the scenes out of the focus range or take them ambiguously.
To address the above problem, camera phones with zoom lens for effecting macro photography have been designed. Various focusing devices of zoom lenses capable of focusing to a macro photographing distance range just beyond the close distance position in a normal photographing distance range which enables zoom magnification change have been proposed and are already known. These focusing devices are disclosed in U.S. Pat. Nos. 4,720,182; 4,806,000; 6,778,333 and U.S. Pat. Pub. No. 20040263999.
A zoom lens in which zoom magnification change and focusing from the normal photography area to the macro area can be accomplished by an operation member is also known, for example, from U.S. Pat. No. 4,448,496. In the above-described prior art, there is shown a zoom lens in which focusing in the normal photography area is accomplished by rotating an operating member and subsequently focusing in the macro area can be accomplished by further rotation of the operating member beyond the normal photography area. However, the mechanical operating device for the above-described conventional zoom lens is rather complicate and thus occupies a large space, which deviates from the miniaturization trend of modern consuming products such as camera phones.
The components of a conventional zoom lens assembly with macro photography capabilities are illustrated in FIGS. 1-2. The conventional zoom lens assembly includes a base 6, a macro ring 7, a focus ring 8, a lens holder 9, a helicoidal spring 10, an outer cap 11, a pair of bolts 12 and an image sensing element 13. The base 6 has an annular socket 61 formed at a central portion thereof for supporting the macro ring 7 therearound and for receiving the focus ring 8 and the lens holder 9 therein. A pair of opposing guide posts 62 and a pair of opposing retention portions 63 are formed at corners of the base 6. Each retention portion 63 defines a threaded hole 65 therein for engaging with the bolt 12, thereby assembling the components into a unit. An opening 66 is defined in the bottom of the base 6 in communication with the annular socket 61 chamber. Three inverted U-shaped supporters 64 are arranged at equal intervals around the outer periphery of the annular socket 61. The macro ring 7 has a bottom surface 72, three projections 71 downwardly projecting from the bottom surface 72, and a transition slope 74 connecting the bottom of each projection 71 with the bottom surface 72. A driving arm 73 projects outwardly from the outer periphery of the macro ring 7. The focus ring 8 includes a barrel 81 for receiving the lens holder 9 therein, a top rim 82 having an outer diameter larger than that of the barrel 81, and a pair of opposite guide portions 83 outwardly projecting from the top rim 82 and each defining a semicircular guide slot 84 therethrough. The image sensing element 13 is a CCD (Charge-Coupled Device) sensor or a CMOS (Complimentary Metal-Oxide Semiconductor) sensor.
A side view of the conventional zoom lens assembly in an assembled state is shown in FIGS. 3 and 4. It should be noted that, for facilitating description of the operation process of the mechanical operating device of the conventional zoom lens assembly, the helicoidal spring 10, the outer cover 11, the bolts 12 and the image sensing element 13 are omitted from FIGS. 3 and 4. As shown in FIGS. 3 and 4, the macro ring 7 is mounted over the annular socket 61 of the base 6. In a normal photographing position as shown in FIG. 3, the bottom surface 72 of the macro ring 7 is supported on the supporters 64 of the base 6. The focus ring 8 with the lens holder 9 received therein is inserted into the annular socket 61 with the rim 82 thereof abutting against the top edge of the macro ring 7. The semicircular guide slots 84 of the focus ring 8 receive corresponding guide posts 62 of the base 6 therein so as to allow upward and downward movements of the focus ring 8. When macro photography is desired, the driving arm 73 of the macro ring 7 is rotated leftwardly as viewed from FIG. 3 from the normal photographing position of FIG. 3 to the macro photographing position of FIG. 4, where the bottoms of the projections 71 of the macro ring 7 are supported on the supporters 64 of the base 6. That is, the macro ring 7 rotates in a certain angle whereby the slope 74 slides over the supporter 64 and then the bottom of the projection 71 engages with the supporter 64. As a result, the focus ring 8 coupled to the macro ring 7 and the lens holder 9 received in the focus ring 8 are both upwardly moved a certain distance, whereby focus length adjustment is achieved and thus macro photography is effected. As illustrated in FIG. 5, in the case of a fixed position of the image plane “M” (i.e., where the image sensing element 13 is arranged) of the optical system, when the object to be photographed is at a normal distance, the lens holder 9 is located at position “L”, and a clear image A′-B′ of such an object A-B is formed on the image plane “M”. When the object to be photographed is at a close-up distance less than a normal object distance, the lens holder 9 is moved from the position “L” to position “L1”, and a clear image A1′-B1′ of such an object A1-B1 is also formed on the image plane “M”.
Although the conventional zoom lens assembly as described above is capable of macro photography by the adoption of a mechanical adjustment device, it requires a number of components and thus is complex in configuration, which results in increased costs and bulky configuration of the zoom lens assembly and thus the photographic device applying such a zoom lens assembly. This deviates from the miniaturization trend of modern consuming products and thus restricts wide application of such a zoom lens assembly.
Further, in the conventional zoom lens assembly as described above, there are provided both a focus ring for the normal photography and a macro ring for the macro photography (an operating member for zoom magnification change). Therefore, when photography is to be continuously effected from the normal photography area to the macro photography area or from the macro photography area to the normal photography area, the two rings must be operated cooperatively. Accordingly, the operation for focusing is complicated and quick focusing cannot be accomplished. In addition, the focusing is discontinuous and this leads to the possibility of missing the opportunity to photograph an object in motion whose distance gradually changes.